In the field of thin film transistor liquid crystal display (TFT-LCD), the coating technology of alignment film mainly comprises inkjet and transfer print. Currently, inkjet is commonly used in the line current generation.
The raw material for fabricating the alignment film is generally a mixture material of polyamic acid (FAA) and soluble polyimide (SPI) with a certain proportion.
During fabricating, firstly, the mixture material is coated on a substrate by a nozzle of an inkjet device. Then, the coated substrate is transferred to a curing device by a robot arm. During curing process, a PAA layer and an SPI layer are formed simultaneously utilizing different curing rates of the PAA material and SPI material. The PAA layer is configured to prevent the contamination from other resin layer or metal layer, and the SPI layer is configured to perform an alignment on the liquid crystal molecules. Finally, the SPI layer is performed with a rubbing alignment to form the alignment film.
However, the present inventors recognized that the separating of the mixture material can not be achieved simply by a heating and curing method. At the same time, the PAA layer and the SPI layer do not have a smooth interface, which causes a non-uniform distribution of the SPI layer. Therefore, a Mura appears on the display panel. In addition, the thickness of the respective layers can not be accurately controlled during forming the alignment film.